The present invention relates to a calcium absorption enhancing agent and a method for producing it.
According to the National Nutrition Survey, an average of Japanese daily calcium intake is still lower than the recommended daily amount. Moreover, a disease resulting from calcium deficiency such as osteoporosis or the like is becoming one of the serious adult diseases. Therefore, it is an important subject for maintaining health of Japanese people to increase calcium intake.
For this purpose, various calcium preparations have been developed. For example, there have been developed calcium preparations containing powder produced by grinding bone of a fish or an animal, egg shell, shell or the like; a calcium salt, or the like, as well as calcium enriched foods to which one or more of the above-mentioned calcium preparations are added, which are commercially available.
However, since the amount of calcium absorption in intestines is small, it is not enough to take calcium. Therefore, it is desired to develop a calcium absorption enhancing agent for accelerating calcium absorption. It is supposed that a substance which weakly binds to a large amount of calcium, and prevents it from precipitating in intestines and being excreted without being absorbed may be effective as a substance for accelerating calcium absorption in intestines.
Casein phosphopeptide (CPP) is known as such a substance. CPP is a substance generated in a process of digestion of casein which exists in cow""s milk. Sour milk beverages to which CPP is added as a calcium absorption enhancing agent have been developed, and are marketed.
However, since CPP is a peptide originating from cow""s milk, it has a so-called cow""s milk flavor. Furthermore, it has poor processing characteristics, and is hardly applied to products other than dairy products such as sour milk beverages. Accordingly, there is a problem that a person who hardly drinks cow""s milk and sour milk beverages cannot take it. It has been desired strongly to develop a calcium absorption enhancing agent which can be applied to a still wider scope of products.
From such a view point, calcium absorption enhancing agents other than CPP have been studied, and soybean protein has been proposed as one of them. However, it has been reported that although a soybean protein has high affinity for calcium, a calcium absorption enhancing effect thereof in vivo is low (Br. J. Nutr., 43, 457-467, 1980; J. Nutr. Sci. Vitaminol., 32, 67-76, 1986). It may be because phytic acid binding to soybean protein may bind to calcium in a digestive tract, to form a water insoluble salt which cannot be absorbed from intestinal wall.
Not only soybean protein, but other vegetable proteins such as proteins of legumes, cereals or the like contain a large amount of acidic amino acids which can bind to calcium weakly. Accordingly, they also seem to be desirable as a calcium absorption enhancing agent. However, a calcium absorption enhancing effect thereof is not high in vivo. One of the reasons may be that many of the acidic amino acids exists as an acid amide form, which cannot bind to calcium as it is.
The inventor of the present invention has noticed that it is advantageous to remove phytic acid and to remove amino groups of acid amide groups in advance, to improve calcium absorption enhancing effect, when using vegetable protein such as soybean protein as a raw material of a calcium absorption enhancing agent, and has developed a soybean protein wherein phytic acid is removed with an anion exchange resin and deamidation is achieved with an enzyme (H. Kumagai et al. Biosci. Biotechnol. Biochem., 62 (2), 341-346, 1998).
However, cost of the deamidation of soybean protein with enzyme is high, and the amount of amide which can be removed is only about 80 xcexcmol/g, which is not enough. The inventor of the present invention has studied further, and found that when the deamidation treatment of vegetable protein was performed using weakly acidic cation exchange resin, deamidation can be performed very efficiently. Thereby, the present invention has been completed.
The present invention provides the following calcium absorption enhancing agents.
(1) A calcium absorption enhancing agent produced by subjecting a vegetable protein to at least a treatment of removing a phytate with an anion exchange resin and a deamidation treatment with a weakly acidic cation exchange resin.
(2) The calcium absorption enhancing agent of (1) wherein the vegetable protein is a soybean protein.
(3) The calcium absorption enhancing agent of (1) wherein the deamidation treatment with the weakly acidic cation exchange resin is conducted at a temperature in the range of 0-50xc2x0 C.
(4) The calcium absorption enhancing agent of (2) wherein the deamidation treatment with the weakly acidic cation exchange resin is conducted at a temperature in the range of 0-50xc2x0 C.
(5) The calcium absorption enhancing agent of (1) wherein the weakly acidic cation exchange resin has carboxyl groups as an exchange group.
(6) The calcium absorption enhancing agent of (2) wherein the weakly acidic cation exchange resin has carboxyl groups as an exchange group.
(7) The calcium absorption enhancing agent of (3) wherein the weakly acidic cation exchange resin has carboxyl groups as an exchange group.
(8) The calcium absorption enhancing agent of (4) wherein the weakly acidic cation exchange resin has carboxyl groups as an exchange group.
Moreover, the present invention relates to the following method for producing a calcium absorption enhancing agent.
(9) A method for producing a calcium absorption enhancing agent wherein a vegetable protein extracted from a plant is subjected to at least a treatment of removing a phytate with an anion exchange resin and a deamidation treatment with a weakly acidic cation exchange resin.
(10) The method for production of (9) wherein the deamidation treatment with the weakly acidic cation exchange resin is conducted at a temperature in the range of 0-50xc2x0 C.
Moreover, the present invention relates to the following calcium enriched foods, the following nutrition compositions for calcium enrichment, and the following pharmaceuticals.
(11) A calcium enriched food which contains the calcium absorption enhancing agent of (1).
(12) A calcium enriched food which contains the calcium absorption enhancing agent of (4).
(13) A calcium enriched food which contains the calcium absorption enhancing agent of (6).
(14) A nutrition composition for calcium enrichment which contains the calcium absorption enhancing agent of (1).
(15) A nutrition composition for calcium enrichment which contains the calcium absorption enhancing agent of (4).
(16) A nutrition composition for calcium enrichment which contains the calcium absorption enhancing agent of (6).
(17) A pharmaceutical preparation which contains the calcium absorption enhancing agent of (1).
(18) A pharmaceutical preparation which contains the calcium absorption enhancing agent of (4).
(19) A pharmaceutical preparation which contains the calcium absorption enhancing agent of (6).